1. Field of Application
The present invention relates to an intersection judgement apparatus and program, for judging when an object located ahead and to one side of a vehicle is moving laterally to intersect with the motion path of the vehicle.
2. Description of Related Art
Types of pre-crash safety system (abbreviated in the following to PCS) are known for installation on a vehicle (referred to in the following as the host vehicle). Such a system can detect a target object such as another vehicle, obstacle, pedestrian, etc., based on information obtained from a radar apparatus and/or an imaging (camera-based) system. The system can for example calculate the TTC (time to collision), i.e., the time remaining until the host vehicle will collide with the target object, by dividing the distance between the host vehicle and the target object by their relative speed. If it is judged based on the TTC that there is a high risk of collision, the PCS can take actions such as generating warnings to the driver of the host vehicle, executing automatic braking of the vehicle, etc., for attempting to prevent the collision.
It is necessary for a PCS to take such actions when a target object is located directly ahead of the host vehicle. However such actions are also necessary when an object such as a pedestrian is positioned ahead of the host vehicle, outside the travel path of the host vehicle, but is becoming successively displaced along a lateral intersection direction (a direction oriented towards and at right angles to the advancement direction of the host vehicle).
The PCS may be configured to detect such a circumstance. However when the host vehicle is being driven for example along a city street where there are many pedestrians, the following problem may arise with the prior art. If the PCS attempts to obtain TTC values for all of the nearby pedestrians who are located ahead of the host vehicle, at the left and right sides of the vehicle travel path, then even when a detected pedestrian moves only momentarily along a lateral intersection direction for a short distance, the PCS may take actions such as generating warning indications, executing automatic braking, etc., which are unnecessary. Hence in such a case, the pedestrians may become obstructions to the progress of the vehicle.
There is thus a requirement for a type of PCS having increased reliability of judging whether a target object such as a pedestrian is actually becoming significantly displaced along a lateral intersection direction, for ensuring that the PCS does not take actions such as generating warning indications, etc., when these actions are unnecessary. Such an improvement of a PCS is referred to in the following as an “improvement of the off performance”.
As a measure for improving the off performance of a PCS, it has been proposed for example in Japanese patent publication No. 2008-197720 as described referring to a second embodiment, that amounts of lateral displacement of a pedestrian towards the advancement direction of the host vehicle are successively detected. If a detected amount of lateral displacement exceeds a threshold value TH1, a warning indication is generated. Each amount of lateral displacement is calculated as an absolute value of a displacement vector, oriented towards and at right angles to the advancement direction of the host vehicle.
Although a radar apparatus or camera apparatus of such a prior art PCS may momentarily detect a target object such as a pedestrian moving in a lateral intersection direction, in many cases it is not possible to continuously detect the motion of the target object. This can occur for example when the object enters a blind spot (i.e., a position at which the field of view of the radar apparatus and/or camera apparatus of the host vehicle becomes partially or completely obstructed by some obstacle, etc.). In such a case, the PCS may not take necessary actions such as generating warning indications, etc., when required.
However if it is attempted to reduce that danger, by relaxing the conditions which must be satisfied before the PCS takes actions such as generating warning indications (e.g., by lowering the threshold value used to judge the magnitudes of obtained values of lateral displacement) there is an increased possibility that the PCS will take such actions unnecessarily, so that the off performance of the PCS will deteriorate.